COMPRESSION AND TENSION TESTS ON AN OPEN-ENDED TUBE PILE IN CHALK

The results of compression and tension tests on an open ended steel tube pile driven into chalk at Immingham, Humberside, are compared with both the recommendations of CIRIA Report PG6, "Piling in Chalk", and the test results from a similar pile in Brighton. Only the results from the former test pile appear consistent with PG6. The differences between the results for the two test piles are considered qualitatively in terms of differences in the chalk at the two sites and the changes which it undergoes during pile driving. Analysis of the results for the Immingham test pile shows it to perform largely as would be expected from the design rules given in CIRIA Report PG6 for a low displacement driven pile. This is notwithstanding that the N values in the Immingham type A chalk far exceed those considered in PG6. For the Immingham test pile the internal shaft resistance is calculated to be about 60% of that developed externally. The Immingham results do not of themselves justify the use elsewhere of the PG6 design rules for chalk with high N values. On the contrary the Brighton pile appears to defy the PG6 rules which would lead to a significant underestimate of the measured shaft resistance. Preliminary loading tests for driven piles founding in strong unweathered chalk are therefore considered to be eseential. Consideration of the type of chalk surrounding a pile and the changes it suffers during pile driving offer a qualitative explanation of the differences between the Immingham and Brighton test pile results.